Using scanning calorimetry, structural transitions of the human erythrocyte membrane are being examined. The particular components of the membrane which are involved in each of these transitions have been identified in the case of several transitions. It have been shown that at least one of the transitions is probably a lipid melting transition, while two others are due to protein unfolding. Since specific inhibitors of anion transport cause large shifts in the phospholipid transition, it appears that the membrane region involved in that transition may be a part of the transport site.